slub: fix per cpu kmem_cache_cpu array memory leak

The per cpu array of kmem_cache_cpu structures accomodates
NR_KMEM_CACHE_CPU such structs.

When this array overflows and a struct is allocated by kmalloc(), it may
have an address at the upper bound of this array.  If this happens, it
does not get freed and the per cpu kmem_cache_cpu_free pointer will be out
of bounds after kmem_cache_destroy() or cpu offlining.

Cc: Christoph Lameter <cl@linux-foundation.org>
Signed-off-by: David Rientjes <rientjes@google.com>
Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>

diff --git a/mm/slub.c b/mm/slub.c
index 6392ae5..bdc9abb 100644 (file)
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1996,7 +1996,7 @@ static struct kmem_cache_cpu *alloc_kmem_cache_cpu(struct kmem_cache *s,
 static void free_kmem_cache_cpu(struct kmem_cache_cpu *c, int cpu)
 {
        if (c < per_cpu(kmem_cache_cpu, cpu) ||
-                       c > per_cpu(kmem_cache_cpu, cpu) + NR_KMEM_CACHE_CPU) {
+                       c >= per_cpu(kmem_cache_cpu, cpu) + NR_KMEM_CACHE_CPU) {
                kfree(c);
                return;
        }